Improving cottonseed oil while preparing the seed for oil extraction



IMPROVING COTTONSEED OIL WHILE PREPAR- ING THE SEED FOR OIL EXTRACTION William H. King and Francis H. Thurber, New Orleans,

La., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Application November 3, 1953, Serial No. 390,098

2 Claims. (Cl. 260412.3)

(Granted under Title 35', U. S. Code (1952), see. 266) A non-exclusive, irrevocable, royalty-free license in the invention herein described, for all governmental purposes, throughout the world, with the power to grant sublicenses for such purposes, is hereby granted-to the Government of the United States of America.

This invention relates to a process of improving the color stability characteristics of cottonseed oil. More particularly, the invention provides a process of treating cottonseed meats containing free gossypol, while they are being prepared for oil extraction, to produce prepared means which yield cottonseed oils having little tendency to undergo color reversion.

Cottonseed contains a number of highly colored pigments such as gossypol, carotenoids and related substances, and the oil extracted from the seed often contains appreciable amounts of these pigments. It is known that a prompt alkali refining and adsorbent bleaching of crude cottonseed oil generally removes the pigments. However, because of the distances between many of the mills where the oil is extracted and the plants where the oil is refined, it is often necessary to store crude cottonseed oils for several months prior to refining. During the storage, pigments such as free gossypol and related materials often undergo chemical changes of such a nature that they can no longer be removed from the stored oils with alkali. This phenomenon is known as color reversion. When an oil has undergone color reversion, the ordinary refining and bleaching procedures fail to remove the colored, chemically changed gossypol thereby resulting in the production of low grade oils which sell at a lower price and to a more limited market than those commanded by the higher grade oils. The high grade oils preferably have a very low refined and bleached color and oils having a color of more than about 3 Lovibond red units tend to have a more limited market.

An object of this invention is to provide a process of materially reducing the amount of free gossypol and the like substances which becomes dissolved in cottonseed oil in the course of its extraction from the seed and thus to provide a process of producing an improved cottonseed oil having little, if'any, tendency to undergo color reversion. A further object is to provide a cottonseed meat treatment process which can be accomplished in the course of the usual cottonseed meat preparation processes using the usual cottonseed treating apparatus. Further objects and advantages will be apparent from the description in the specification and claims.

In general, according to the process of this invention, cottonseed meats containing free gossypol are converted to meats which yield cottonseed oils having little tendency to undergo color reversion by mixing raw cottonseed meats with from about 0.5 to 2.5% of their weight of an alkali metal hydroxide in the form of an aqueous solution, and heat treating the meats to enhance the availability of the cottonseed oil while the meats are in contact with the aqueous alkali metal hydroxide. The eifec-t of this process is to react the gossypol with the aqueous alkali metal hydroxide to form Water-soluble and oil-insoluble derivatives before much of the gosspol becomes dissolved in a continuous oil phase of appreciable volume.

The use of the specified amount of aqueous alkali metal hydroxide, and the steps of mixing the hydroxide: with raw cottonseed meats prior to an oil-coalescing heat.

treatment of the meats, are necessary in order to obtain the improved oils.

Two early Phillips patents, Numbers 705,785 and 1,347,870, specify treatments of cottonseed meats with, respectively, from about 0.04 to 0.2%, and about 0.01% by weight of an alkali metal hydroxide in the form of an aqueous solution. However, we have found that the meats prepared by such treatments, using appreciably less than about 0.5% alkali metal hydroxide, in the absence of severely cooking and/or agitating the meats to rupture the pigment glands and bind the. gossypol to the meal components, yield oils exhibiting an appreciable tendency to undergo color reversion.

A publication by Wamble, Oil Mill Gazetteer, February 1943, pp. 2-224, reports that adding soda to cottonseed meats in the cooker or adding sodium carbonate. to raw rolled cottonseed meats failed to accomplish either the anticipated reduction in the free fatty acid content of the oil or to reduce the red color of the oil.

We have discovered that in order to obtain the improved oils, substantially all'of the; gossypol containing pigment glands contained in the cottonseed meats must be brought into intimate contact with suflicient aqueous alkali metal hydroxide to react with substantially all of the gossypol they contain. Some gossypol pigment glands are ruptured during most of the processing steps used in the prepartion of cottonseed meatsfor oil extraction. In order to obtain the improved oils, substantially all of the gossypolv released by the. rupture of the pigment glands,

that is, the free gossypol must be reacted with the aqueous alkali metal hydroxide. to form water soluble and oil insoluble derivatives before much of the gossypol be comes dissolved in a continuous oil phase of appreciable volume. Generally most of the pigment glands which are ruptured in a given cottonseed meat preparation process are ruptured by the continued action of heat and mechanical agitation during the heat treating of the meats in the usual oilseed heating devices. And, in such a heat treatment, an appreciable amount of the oil contained in the meats is coalesced into a continuous oil phase of an appreciable volume. It the gossypol pigment glands which are ruptured during the heat treatment are in con tact with sufficient aqueous alkali metal hydroxide, little,

if any. gossypol becomes dissolved in the oil.

In accordance with the process of the present invention, any of the alkali metal hydroxides can be used but, primarily for economic reasons, the use of sodium hydroxide is preferred.

The raw meats can be mixed with the aqueous hydroxide at any stage prior to the heat treatment of the meats, but it is preferable to mix the meats, with the aqueous hydroxide as soon as they have been dehulled and comminuted to relatively small particles. The mixing can be accomplished by immersing the meats in the aqueous solution containing the hydroxide or by spraying the aqueous solution onto the meats as long as it is accompanied by suflicient agitation to obtain a substantially complete distribution of the aqueous hydroxide throughout all of the meat particles. Any apparatus, capable of providing a uniform mixing of solid particles with an aqueous solution can be used.

The concentration of hydroxide in the aqueous solution containing it can be varied widely. In general it is preferable to mix the meats with an amount of the aqueous solution, of whatever concentration, sufficient to bring the meats into contact with from about 0.75 to 1.5% of their weight of the alkali metal hydroxide. The use of relatively dilute solutions, containing from about 5 to of the hydroxide, is preferred where the cottonseed meats contain from about 6 to 12% moisture, and, in such a case, the mixing increases the moisture content of the meats to from about to In general, the concentration of the hydroxide in the aqueous solution containing it is preferably selected so that mixing the meats with the desired amount of hydroxide results in an increase in the meat moisture content to the desired range for the heat treatment and for any other treatments to which the meats are to be subjected in the course of their preparation for oil extraction.

A wide variety of conditions can be used in heat treating the cottonseed meats mixed with alkali metal hydroxide in accordance with this invention. In general, any heat'treatment in which the meats are subjected to suflicient heat and agitation to coalesce an appreciable amount of the oil into a continuous oil phase can be used. A preferred treatment comprises heating meats containing about 15 to 25% moisture at increasingly higher temperatures ranging from about 170 to 235 F. while dehydrating the meats to a moisture content from about 4 to 7% where the oil is to be extracted by press ing, and to a moisture content of from about 7 to 11 where the oil is to be solvent extracted. In general, any of the conventional methods and apparatus for heat treating cottonseed meats can be used, but the use of the relatively mild dehydrative cook is advantageous in that it tends to restrict the amount of protein damage, and thus, to result in the production of extracted meals of greater value.

As will be apparent to those skilled in the art, the process of the present invention is uniquely adapted for incorporation into substantially any of the presently used procedures for preparing cottonseed meats for oil extraction, with little or no change in apparatus. Light colored oils having little tendency to undergo color reversion can be extracted from cottonseed meats prepared in accordance with this invention either by means of pressing and/ or by means of solvent extraction with the conventional oil solvents such as the commercial hexanes, the methylpentanes, and the like. Solvent extraction is preferred.

Our co-pending application, Serial No. 373,926, filed August 12, 1953, relates to a process of preparing cottonseed meats for oil extraction. In that process, a step of mixing cottonseed meats with a relatively large amount of an aqueous liquid is combined with a step of subjecting the moistened meats to a particularly severe mechanical agitation to rupture substantially all of the gossypol glands contained in the meats. The use of the amounts of alkali metal hydroxide herein specified in the process of that co-pending application provides not only the improvements in oil herein described but also the improvements in the extracted meal which are dethe invendehydratively heat treated at a temperatures of from to 212 F. for times of from 30 to 60 minutes, to provide prepared meats containing from about 4 to 11% moisture. The oil contained in the so prepared meats were extracted with hexane and desolventized, using conventional procedures and apparatus.

The free gossypol content and the red color (in Lovibond units) of the so-extracted oils, after the crude oils were stored for the indicated periods of time under the usual cottonseed oil storing conditions and refined and bleached using conventional methods and apparatus, are reported in the table.

Table Percent Percent Crude Percent Moisture Gossypol Oil Refined NaOH in lye in crude Storage and treated 011 time, Bleached meats months Color None 25 0. 30 2-3 75. 4 0. 07 25 0.39 2-3 16. 8 0. 4 p 25 0.07 2-3 5. 8 None 16 0. 33

The foregoing data show that treatment of cottonseed meats with 0.5 to 2.0% lye yield oils of 0.00 to 0.06% gossypol which refine and bleach to colors of 0.9 to 2.9 Lovibond red units after 2-3 months storage. Meats similarly treated with less than 0.5%, or no alkali, yield oils of 0.07 to 0.39% gossypol which give refined and bleached colors after storage ranging from 5.8 to 75.4 red units.

We claim:

1. A process of converting cottonseed meats containing free gossypolto mildlycooked meats in which the said free gossypol has been changed to water-soluble and oil-insoluble derivatives thus yielding cottonseed oils having little tendency to undergo color reversion, comprising mixing fiaked raw cottonseed meats containing free gossypol with aqueous alkali metal hydroxide of such concentration as to result in a mixture containing from about 0.5 to 2.5% of the weight of the meats of alkali metal hydroxide and containing an amount of water which increases the moisture content of the mixture to from about 15 to 25 and dehydratively cooking the mixture, at increasingly higher temperatures between from about to 235 E, to reduce the moisture content of the mixture to from about 4 to 11%.

2. The process of claim 1 in which the aqueous alkali is a water solution containing from 5 to 10% sodium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS OF CONVERTING COTTONSEED MEATS CONTAINING FREE GOSSYPOL TO MILDLY COOKED MEATS IN WHICH THE SAID FREE GOSSYPOL HAS BEEN CHANGED TO WATER-SOLUBLE AND OIL-INSOLUBLE DERIVATIVES THUS YIELDING COTTONSEED OILS HAVING LITTLE TENDENCY TO UNDERGO COLOR REVERSION, COMPRISING MIXING FLAKED RAW COTTONSEED MEATS CONTAINING FREE GOSSYPOL WITH AQUEOUS ALKALI METAL HYDROXIDE OF SUCH CONCENTRATION AS TO RESULT IN A MIXTURE CONTAINING FROM ABOUT 0.5 TO 2.5% OF THE WEIGHT OF THE MEATS OF ALKALI METAL HYDROXIDE AND CONTAINING AN AMOUNT OF WATER WHICH INCREASES THE MOISTURE CONTENT OF THE MIXTURE TO FORM ABOUT 15 TO 25%, AND DEHYDRATIVELY COOKING THE MIXTURE, AT INCREASINGLY HIGHER TEMPERATURES BETWEEN FROM ABOUT 170 TO 235*F., TO REDUCE THE MOISTURE CONTENT OF THE MIXTURE TO FORM ABOUT 4 TO 11%. 